1. Institute of Tropical Agriculture and Food Security, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
2. Department of Poultry Production, Faculty of Animal Production, University of Khartoum, 13314 Khartoum North, Sudan
3. Department of Animal Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia; Department of Veterinary Pathology and Microbiology, Faculty of Veterinary Medicine, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
4. Department of Dairy Production, Faculty of Animal Production, University of Khartoum, 13314 Khartoum North, Sudan